Push-type strapping tools are known which achieve tension by pushing against a seal which has been threaded on overlapping strap portions with the free end of the strap bent back under the seal. A manually operated tool of this type is disclosed in the U.S. Pat. No. 3,844,317 to Angarola et al. A power-operated type of tool which automatically tensions and subsequently crimps or notches the seal is marketed by Brainard Strapping Division, NVF Corporation under the designation PNRDPA.
Another type of power-operated, push-type tool, which is pneumatically-operated, is disclosed in the U.S. Pat. No. 3,329,178 to Plunkett. The tool disclosed in the Plunkett patent is actuated by the tool user or operator to tension the loop about the article and is then subsequently actuated a second time by the operator to crimp the seal around the overlapping strap segments.
In some applications, particularly those involving thermally hot articles such as coils or hot steel, it would be desirable to have a push-type strapping tool that need by activated only once by manually operating a switch or lever so that the tool then automatically tensions the strap loop, crimps or notches the seal about the overlapping strap portions, severs the trailing portion of the strap from the tensioned and sealed loop, and then retracts the mechanisms as may be necessary to permit the tool to be removed from the tensioned strap loop. A tool which would automatically effect the various operations would be safer under such conditions because the operator of the tool could move away from a hazardous environment while the tool is cycling. The tool would be more efficient because the operator could perform other tasks while the tool is cycling.
The above-described Brainard Strapping Division PNRDPA tool automatically initiates the various sequences, and in particular, automatically initiates the sealing sequence upon sensing the pressure rise in the air line to an air motor. It would be desirable to provide a tool in which a predetermined tension level could be positively sensed by the movement of a member, which movement would be directly effected by the tension in the strap acting through a rigid engagement of the member with the strap seal. It would also be beneficial to provide a means that could be easily adjusted to vary the predetermined tension level at which the tool would initiate the sealing sequence.